Rolled h-section steel

ABSTRACT

Provided is a rolled H-section steel having a web and flanges. The rolled H-section steel satisfies the following Expression (1) when H is the height of the rolled H-section steel, and B is the breadth of the flanges. The tensile strength is 400 to 510 N/mm 2 . The rolled H-section steel satisfies the following Expressions (2) and (3), when the plate thickness of the flanges is t 2 , and the design yield stress of a steel material of the rolled H-section steel is F(N/mm 2 ). 
       ( B/H )≦0.77  (1)
 
       11.1&lt; B /(2× t   2 )≦215/√{square root over ( )}( F )  (2)
 
       235≦ F ≦275  (3)

TECHNICAL FIELD

The present invention relates to a rolled H-section steel that directly supports a floor slab or roof floor slab, and is applied to a small beam that is not directly connected to a pillar, a beam that is used within an elastic design range, and the like.

Priority is claimed on Japanese Patent Application No. 2009-162402, filed Jul. 9, 2009, the content of which is incorporated herein by reference.

BACKGROUND ART

Conventionally, as rolled H-section steels, various rolled H-section steels like the following (1) to (5) are known.

(1) A rolled H-section steel having excellent earthquake resistance, in which the flange breadth-thickness ratio is less than or equal to 10, the work-hardening exponent in a strain range up to 6% after work-hardening is started is greater than or equal to 0.2, and the rising gradient of plastic deformation stress in a strain range of 6% or more is larger than the moment gradient in the vicinity of a position having a maximum moment, whereby a plastic region generated at a position that causes the maximum moment is enlarged to the perimeter (for example, refer to Patent Document 1).

(2) A rolled H-section steel for a pillar in which the web thickness to flange thickness ratio is 1.2 to 4, and reinforcement by a doubler plate in a pillar-to-beam joint panel, an oblique stiffener, or the like (for example, refer to Patent Document 2) can be omitted.

(3) A rolled H-section steel for a pillar in which the web thickness to flange thickness ratio is 1.1 to 2.0, and reinforcement by a horizontal stiffener at a beam flange joining position in a pillar-to-beam joint, a doubler plate in a panel, an oblique stiffener, or the like can be omitted (for example, refer to Patent Document 3).

(4) A thin-web rolled H-section steel in which the web thickness to flange thickness ratio is less than or equal to 0.5, and concavo-convex are formed at predetermined intervals in a web in order to prevent a web flapping phenomenon during rolling (for example, refer to Patent Document 4).

(5) A thin-web rolled H-section steel in which the web thickness to flange thickness ratio is less than or equal to 0.5, and at least one protrusion reinforcing rib is provided over the longitudinal total length of only one lateral surface of a web in order to prevent a web flapping phenomenon during rolling (for example, refer to Patent Document 5).

Additionally, as techniques regarding conventional rolled H-section steels, techniques like the following (A) to (D) are also known.

(A) Since it is necessary to secure the plastic deformation capacity of a rolled H-section steel in order to be used as a pillar or beam member having excellent earthquake resistance, as shown in JIS G 3192 or Patent Document 6, the flange breadth-thickness ratio and the web breadth-thickness ratio are specified in a relatively small numerical range (the upper limit of the flange breadth-thickness ratio is set to 10.0 and the upper limit of the web breadth-thickness ratio is set to 56.6, according to JIS, in a case where a major application is a beam and the side-height ratio is in a range of 0.77 or less) that is said to have a deformation capacity.

(B) In order to improve the cross-sectional secondary moment and the section modulus to weight efficiency, the web thickness to flange thickness ratio of a rolled H-section steel for a beam is specified in a relatively small numerical range (the upper limit of the web thickness to flange thickness ratio is set to 0.75, in a case where a major application is a beam and the side-height ratio is in a range of 0.77 or less) as being specified in JIS G 3192.

(C) In order to omit reinforcement by a doubler plate in a pillar-to-beam joint panel, an oblique stiffener, or the like, it is also known that the web thickness to flange thickness ratio of a rolled H-section steel for a pillar is specified in a relatively large numerical range (the lower limit of the web thickness to flange thickness ratio is set to 1.1) (for example, refer to Patent Documents 2 and 3).

(D) In order to realize a thin-web rolled H-section steel while preventing the web flapping phenomenon during rolling manufacture, it is also known that the web thickness to flange thickness ratio is specified in a relatively small numerical range (the upper limit, of the web thickness to flange thickness ratio is 0.5) (for example, refer to Patent Documents 4 and 5).

(E) In addition to the above, there are rolled H-section steels that are standardized in ASTM (American Society for Testing and Materials), BS (British Standards), and EN (European Standard) (refer to Non Patent Documents 1 to 3).

Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application, First     Publication No. 2002-88974 -   [Patent Document 2] Japanese Unexamined Patent Application, First     Publication No. 2000-54560 -   [Patent Document 3] Japanese Unexamined Patent Application, First     Publication No. 2003-155779 -   [Patent Document 4] Japanese Unexamined Patent Application, First     Publication No. S59-141658 -   [Patent Document 5] Japanese Unexamined Patent Application, First     Publication No. S61-162658 -   [Patent Document 6] Japanese Unexamined Patent Application, First     Publication No. 2002-88974

Non Patent Documents

-   [Non Patent Document 1] ASTM (American Society for Testing and     Materials) -   [Non Patent Document 2] BS (British Standards) -   [Non Patent Document 3] EN (European Standard)

DISCLOSURE OF INVENTION Technical Problem

The shape of the rolled H-section steel, as described above, is standardized in respective countries including the U.S., Britain, Europe, and Japan. For example, in Japan, various rolled H-section steels described in JIS G 3192 (the shape, dimensions, mass, and allowance of a hot rolled steel) are known.

As for “the shape, dimension, mass, and its allowance of a hot rolled steel in JIS G 3192”, the cross-sectional dimensions in “Appended Table 8: Standard section dimensions and cross-sectional area, unit mass, and cross-sectional characteristics of H-section steel” published in JIS G 3192 are posted in the following Table 1, and the following (a) to (c) can be seen from a side-height ratio (B/H), a flange breadth-thickness ratio (B/(2×t₂)), a web breadth-thickness ratio ((H−2×t₂)/t₁), and a web thickness and flange thickness ratio (t₁/t₂), which are shown in Table 1.

(a) The flange breadth-thickness ratio is in a range of 3.1 to 13.4.

(b) The web breadth-thickness ratio is in a range of 8.0 to 56.6.

(c) The web thickness to flange thickness ratio is in a range of 0.53 to 1.00.

Various conventional rolled H-section steels in which the side-height ratio (B/H) of the various conventional rolled H-section steels in Table 1 is less than or equal to 0.77 are plotted and shown with open circle marks in FIGS. 1 and 4, and various conventional rolled H-section steels in which the side-height ratio (B/H) in Table 1 exceeds 0.77 are plotted and shown with marks X.

FIGS. 1 and 4 are graphs showing the horizontal axis as the flange breadth-thickness ratio (B/(2×t₂)) and showing the vertical axis as the web breadth-thickness ratio ((H−2×t₂)/t₁). Additionally, the various conventional rolled H-section steels shown in Table 1 are plotted and shown in FIGS. 2 and 5 with the horizontal axis as the side-height ratio (B/H) and the vertical axis as the web thickness to flange thickness ratio (t₁/t₂).

Here, the major application of rolled H-section steels in which the side-height ratio is in a range (marketed in Japan as a small-breadth series or middle-breadth series of rolled H-section steels regarding the flange breadth of rolled H-section steel) of 0.77 or less can be classified into a beam, and the major application of rolled H-section steels in which the side-height ratio is in a range (marketed as a large-breadth series of rolled H-section steels regarding the flange breadth of rolled H-section steel) exceeding 0.77 can be classified into a pillar or a brace. In addition, in Table 1 Height×Side (H×B) (unit: mm): 150×100, 200×150, 250×175, 300×200, 350×250, 400×300, 450×300, 500×300, 600×300, 700×300, 800×300, and 900×300 (mm) are middle-breadth series, and the height (H) and the side (B) that has the same dimensions are large-breadth series, and the others are small-breadth series.

Thus, if the major application is a beam, and the side-height ratio is limited to a range of 0.77 or less, the following (d) to (f) can be seen.

(d) The flange breadth-thickness ratio is in a range of 3.1 to 10.0,

(e) the web breadth-thickness ratio is in a range of 17.2 to 56.6, and

(f) the web thickness to flange thickness ratio is in a range of 0.53 to 0.75.

Being set as in the above (d) to (f) is based on the following reasons (g) and (h).

(g) The reason why the flange breadth-thickness ratio is a relatively small numerical range of 17.2 to 56.6 when the web breadth-thickness ratio is in a range of 3.1 to 10.0 is because, if the ratio of the breadth to thickness of a plate element that constitute a member section is large, local buckling is caused in a portion that receives a compressive force, and the proof stress of the member section declines and a required plastic deformation capacity is no longer obtained.

(h) Moreover, the reason why the web thickness to flange thickness ratio is in a relatively small numerical range of 0.53 to 0.75 is because the cross-sectional secondary moment per unit cross-sectional area and the section modulus are increased by thickening flanges and thinning a web since a beam is a member that receives a bending stress.

Additionally, various rolled H-section steels that are standardized in ASTM (American Society for Testing and Materials), BS (British Standards), and EN (European Standard) are divided into various rolled H-section steels in which the side-height ratio (B/H) is in a range of 0.77 or less and various rolled H-section steels in which the side-height ratio (B/H) exceeds 0.77, and the upper limits of the flange breadth-thickness ratio, web breadth-thickness ratio, and web thickness to flange thickness ratio (t₁/t₂) of the various rolled H-section steels in which the side-height ratio (B/H) is in a range of 0.77 or less are shown in FIGS. 6 to 11 for close study.

Additionally, in FIGS. 6 and 7, as for the various rolled H-section steels that are standardized in ASTM (American Society for Testing and Materials), the various rolled H-section steels (rolled H-section steels belonging to the middle breadth or the small breadth) in which the side-height ratio (B/H) is in a range of 0.77 or less are plotted and shown with open circle marks, and the various rolled H-section steels in which the side-height ratio (B/H) exceeds 0.77 are plotted and shown with X marks. A table of the various rolled H-section steels that are plotted and shown in FIGS. 6 and 7 and are standardized in ASTM (American Society for Testing and Materials) is omitted.

FIG. 6 is a graph plotting and showing the various rolled H-section steels that are standardized in ASTM, with the horizontal axis as the flange breadth-thickness ratio (B/(2×t₂)) and the vertical axis as the web breadth-thickness ratio ((H−2×t₂)/t₁). It can be seen from this drawing that, in the rolled H-section steels that are shown with open circles and belong to the middle breadth or the small breadth, the upper limit of the flange breadth-thickness ratio is 9.4, and the upper limit of the web breadth-thickness ratio is 63.5.

Additionally, as for the various rolled H-section steels that are standardized in ASTM, the various rolled H-section steels are plotted and shown in FIG. 7 with the horizontal axis as the side-height ratio (B/H) and the vertical axis as the web thickness to flange thickness ratio (t₁/t₂). It can be seen from this graph that, in the rolled H-section steels that are shown with open circles and belong to the middle breadth or the small breadth, the upper limit of the side-height ratio (B/H) is 0.72, and the upper limit of the web thickness to flange thickness ratio (t₁/t₂) is 0.82.

Additionally, in FIGS. 8 and 9, as for the various rolled H-section steels that are standardized in BS (British Standards), the various rolled H-section steels (rolled H-section steels belonging to the middle breadth or the small breadth) in which the side-height ratio (B/H) is in a range of 0.77 or less are plotted and shown with open circle marks, and the various rolled H-section steels in which the side-height ratio (B/H) exceeds 0.77 are plotted and shown with X marks. A table of the various rolled H-section steels that are plotted and shown in FIGS. 8 and 9 and are standardized in BS (British Standards) is omitted.

FIG. 8 is a graph plotting and showing the various rolled H-section steels that are standardized in BS, with the horizontal axis as the flange breadth-thickness ratio (B/(2×t₂)) and the vertical axis as the web breadth-thickness ratio ((H−2×t₂)/t₁). It can be seen from this drawing that, in the rolled H-section steels belonging to the middle breadth or the small breadth, the upper limit of the flange breadth-thickness ratio is 8.6, and the upper limit of the web breadth-thickness ratio is 63.3.

Additionally, FIG. 9 is a graph shown by plotting the various rolled H-section steels that are standardized in BS (British Standards) with the horizontal axis as the side-height ratio (B/H) and the vertical axis as the web thickness to flange thickness ratio (t₁/t₂). It can be seen from this graph that, in the rolled H-section steels that are shown with open circles and belong to the middle breadth or the small breadth, the upper limit of the side-height ratio (B/H) is 0.66, and the upper limit of the web thickness to flange thickness ratio (t₁/t₂) is 0.86.

Additionally, in FIGS. 10 and 11, as for the various rolled H-section steels that are standardized in EN (European Standard), the various rolled H-section steels (rolled H-section steels belonging to the middle breadth or the small breadth) in which the side-height ratio (B/H) is in a range of 0.77 or less are plotted and shown with open circle marks, and the various rolled H-section steels in which the side-height ratio (B/H) exceeds 0.77 are plotted and shown with X marks. A table of the various rolled H-section steels that are plotted and shown in FIGS. 10 and 11 and are standardized in EN (European Standard) is omitted.

FIG. 10 is a graph plotting and showing the various rolled H-section steels that are standardized in EN (European Standard), with the horizontal axis as the flange breadth-thickness ratio (B/(2×t₂)) and the vertical axis as the web breadth-thickness ratio ((H−2×t₂)/t₁). It can be seen from this drawing that, in the rolled H-section steels belonging to the middle breadth or the small breadth, the upper limit of the flange breadth-thickness ratio is 11.1, and the upper limit of the web breadth-thickness ratio is 58.0. Additionally, the various rolled H-section steels that are standardized in EN (European Standard) is plotted and shown in FIG. 11 with the horizontal axis as the side-height ratio (B/H) and the vertical axis as the web thickness to flange thickness ratio (t₁/t₂). It can be seen from this graph that, in the rolled H-section steels that are shown with open circles and belong to the middle breadth or the small breadth, the upper limit of the side-height ratio (B/H) is 0.77, and the upper limit of the web thickness and flange thickness ratio (t₁/t₂) is 0.78.

Meanwhile, since the number of small beams to be used is large compared to the number of large beams, if the weight per beam can be reduced without degrading the required cross-sectional performance, it is possible to greatly contribute to the reduction of the cost of a main body of a structure even if the cost reduction per beam is small.

For example, if the weight of a small beam or the like can be reduced by 10% or more, without reducing the earthquake-resistent performance of the beam, the unit price of the beam can be reduced by about 10%. Therefore, not only can the cost of the main body of a structure be reduced markedly, but also the weight of the structure can be reduced, and the burden of a pillar becomes smaller to the extent that the weight of the structure is reduced. This also can contribute to improvement in the earthquake-proof performance of a structure.

Moreover, compared to rolled H-section steels that are standardized in major advanced nations including the U.S., Britain, Europe, and Japan, a rolled H-section steel is desired which may be made lightweight for a small beam and which does not degrade the cross-sectional performance. The object of the invention is to provide a rolled H-section steel that is advantageous for solving the above problems.

Solution to Problem

The following means is adopted in order to solve the problems advantageously.

(a) The rolled H-section steel related to one aspect of the invention is a rolled

H-section steel having a web and flanges. The rolled H-section steel satisfies the following Expression (1) when H is the height of the rolled H-section steel, and B is the breadth of the flanges; the tensile strength is 400 to 510 N/mm², the rolled H-section steel satisfies the following Expressions (2) and (3) when t₂ is the plate thickness of the flanges, and the design yield stress of a steel material of the rolled H-section steel is F(N/mm²).

(B/H)≦0.77  (1)

11.1<B/(2×t ₂)≦215/√{square root over ( )}(F)  (2)

235≦F≦275  (3)

(b) The rolled H-section steel described in the above (a) may satisfy the following Expression (4) when the plate thickness of the web is t₁.

63.5<((H−2×t ₂)/t ₁)≦1100/√{square root over ( )}(F)  (4)

(c) In the rolled H-section steel described in the above (a), the plate thickness t₁ of the web and the plate thickness t₂ of the flanges satisfy the following Expression (5).

0.75<(t ₁ /t ₂)<1.0  (5)

Advantageous Effects of Invention

According to the rolled H-section steel described in the above (a), even if a material in which the design yield stress F changed in the above range is used, the flange breadth-thickness ratio of the rolled H-section steels belonging to the small breadth or the middle breadth in the major countries can be specified easily and the cross-sectional shape of the rolled H-section steel can be specified.

Moreover, the weight of this rolled H-section steel can be reduced more than the conventional rolled H-section steels specified in major countries such as the U.S., Britain, Europe, or Japan. Moreover, the cross-sectional performance of this rolled H-section steel can be kept greater than or equal to that of corresponding rolled H-section steels in the these countries. Accordingly, according to this rolled H-section steel, in all the countries of the world including the major countries, dimensions can be easily set and applied.

Additionally, since the flange breadth-thickness ratio (B/(2×t₂)) with the flange breadth B and the plate thickness t2 of the flanges in the rolled H-section steel may be set to the range of the above Expression (2), even if the design yield stress F of a steel material to be used for this rolled H-section steel changes, the flange breadth-thickness ratio (B/(2×t₂)) of the rolled H-section steel can be set easily.

That is, as for this rolled H-section steel, the dimensions of the H-section steel are easily set from the relationship between the height H of the rolled H-section steel, the breadth B of the flanges, the plate thickness t₂ of the flanges, and the design yield stress F (N/mm²) of the steel material. Therefore, the cross-sectional area is reduced without reducing the cross-sectional performance compared to conventional rolled H-section steels, and a rolled H-section steel with a new dimension or shape with reduced weight can be provided.

Additionally, in the case of the above (2), the web breadth-thickness ratio ((H−2×t₂)/t₁) of the rolled H-section steel can be set to a predetermined range from the relationship between the height H of the H-section steel, the plate thickness t₁ of the web, the plate thickness t₂ of the flanges, and the design yield stress F (N/mm²) of the steel material. As a result, the weight of a steel material can be reduced without reducing the cross-sectional performance compared to conventional well-known rolled H-section steels, and a rolled H-section steel with a new dimension or shape can be provided.

For example, in this rolled H-section steel in which dimensions are set as described above, the weight per beam can be reduced more than that of conventional H-section steels by about 10%. As a result, the cost per rolled H-section steel can be reduced, and this can also contribute greatly to reduction of the cost of a structure using this rolled H-section steel. For example, if the weight of a small beam can be reduced by 10% or more, without reducing the earthquake-resistent performance of the beam, the unit price of the small beam can be reduced by about 10%. Therefore, not only can the construction cost of a structure be markedly reduced, but also the weight of the structure can be reduced due to the weight reduction of the small beam, and the earthquake-proof performance can be improved.

Particularly, when applying to rolled H-section steels for a small beam with high versatility, the cross-sectional area can be reduced by about 10% more than conventional rolled H-section steels, and it is possible to provide a small beam having a cross-sectional performance that is greater than or equal to conventional cross-sectional performance. As a result, it is possible to provide an inexpensive small beam, in which the cross-sectional secondary moment can be improved by 15% or more to a maximum of about 60%, and the section modulus is improved, so that at least the section modulus is the same as before, and the best the section modulus achieves improvement of 15%.

Additionally, when the dimensions of the rolled H-section steel are set by a combination of the above (a) to (c), even when the design yield stress F (N/mm²) is broadened to 235≦F≦275 as the specified design strength of the steel material, the weight per rolled H-section steel can be reduced by about at least 5% or more and a maximum of about 15% more than conventional products, and the cost per one rolled H-section steel can be reduced. Hence, it is possible to greatly contribute to the reduction of the construction cost of a structure using this rolled H-section steel. For example, the weight of a small beam can be reduced by about at least 5% or more and a maximum of 15%, without reducing the earthquake-resistent performance of the small beam. Hence, the unit price of the small beam can be reduced by about 5% or more and up to about 15%. Therefore, not only can the cost of a structure be markedly reduced, but also the weight of the structure can be reduced due to the weight reduction of the small beam, and the earthquake-resistent performance can be improved.

This rolled H-section steel is optimal to a rolled H-section steel for a small beam with little weight burden, weight can be reduced by about at least 5% or more and about a maximum of 15% more than conventional rolled H-section steels, and a small beam having the cross-sectional performance that is greater than or equal to conventional cross-sectional performance can be provided. Hence, it is possible to provide an inexpensive small beam in which the cross-sectional secondary moment can be improved by 5% or more and a maximum of about 65%, and the section modulus is improved so that at least the section modulus is the same as before, and the best the section modulus achieves improvement of 20%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the relationship between a web breadth-thickness ratio and a flange breadth-thickness ratio in various rolled H-section steels related to one embodiment of the invention and various rolled H-section steels according to JIS.

FIG. 2 is a graph showing the relationship between a web thickness to flange thickness ratio and a side-height ratio in the various rolled H-section steels related to this embodiment and the various rolled H-section steels according to JIS.

FIG. 3 is a view showing the representative dimensions of parts of a rolled H-section steel and is an outline view as seen in a cross-section perpendicular to a longitudinal direction of the beam.

FIG. 4 is a graph showing the relationship between a web breadth-thickness ratio and a flange breadth-thickness ratio in the various rolled H-section steels according to JIS.

FIG. 5 is a graph showing the relationship between a web thickness to flange thickness ratio and a side-height ratio in the various rolled H-section steels according to JIS.

FIG. 6 is a graph showing the relationship between a web breadth-thickness ratio and a flange breadth-thickness ratio in various rolled H-section steels according to ASTM.

FIG. 7 is a graph showing the relationship between a web thickness to flange thickness ratio and a side-height ratio in the various rolled H-section steels according to ASTM.

FIG. 8 is a graph showing the relationship between a web breadth-thickness ratio and a flange breadth-thickness ratio in various rolled H-section steels according to BS.

FIG. 9 is a graph showing the relationship between a web thickness to flange thickness ratio and a side-height ratio in the various rolled H-section steels according to BS.

FIG. 10 is a graph showing the relationship between a web breadth-thickness ratio and a flange breadth-thickness ratio in the various rolled H-section steels according to EN.

FIG. 11 is a graph showing the relationship between a web thickness to flange thickness ratio and a side-height ratio in the various rolled H-section steels according to EN.

DESCRIPTION OF EMBODIMENTS

Next, one embodiment of a rolled H-section steel of the invention will be described in detail.

First, the representative dimensions of parts in a rolled H-section steel 1 of the present embodiment and a rolled H-section steel 2 of a conventional example is shown in FIG. 3. Reference sign H represents the height (mm) of an H-section steel 1 (2), reference sign B represents the length (mm) of a side that is the flange breadth of H-section steel 1 or 2, reference sign t₁ represents the thickness (mm) of a web 3, reference sign t₂ represents the thickness (mm) of flanges 4, and reference sign r represents the curvature radius R (mm) of inner corners between the web 3 and the flanges 4.

In order to use the rolled H-section steel as a beam is a major application, the relationship between the height H of the H-section steel 1 and the length B (hereinafter, the length of the side is simply referred to as a side) of a side that is the flange breadth in the rolled H-section steel of the present embodiment satisfies the following Expression (1) similarly to the conventional case.

(B/H)≦0.77  (1)

As described above, the reason why the relationship between the height H and the length B of the side that is the flange breadth in the rolled H-section steel 1 is specified is the same as the above-described reason in conventional products. That is, whether a side-height ratio B/H that is the ratio of the height H and the length B of the side that is the flange breadth in the rolled H-section steel 1 is either less than 0.77 or greater than or equal to 0.77 depending on the applications of the beam. That is, since the rolled H-section steel is mainly used as a pillar when this side-height ratio B/H exceeds 0.77, and the rolled H-section steel is mainly used as a beam when the side-height ratio B/H has a middle breadth or small breadth of 0.77 or less, the present embodiment has also adopted such a practical index.

The rolled H-section steel to be targeted in the present embodiment is a rolled H-section steel that is mainly used as a beam in which the side-height ratio B/H falls within 0.77 or less, and the tensile strength of a steel is 400 to 510 N/mm² (the design yield stress F of the steel material is 235 N/mm² to 275 N/mm²). That is, the targeted rolled H-section steel is a rolled H-section steel made of steel materials which are equivalent to SS400 (tensile strength is 400 N/mm² to 510 N/mm²) in JIS G 3101, SM400A, B, C (tensile strength is 400 N/mm² to 510 N/mm²) in JIS G 3106, and SN400A, B, and C (tensile strength is 400 N/mm² to 510 N/mm²) in JIS G 3136.

In addition, the rolled H-section steel of the present embodiment is a rolled H-section steel to be used in the elastic range thereof. For example, if the rolled-H-section steel is used as a small beam, the rolled H-section steel remains in use within the elastic range. Therefore, the required plastic deformation capacity of a beam member is zero (plastic modulus 1.0), which is sufficient.

In this way, the targeted rolled H-section steel 1 in the present embodiment is a rolled H-section steel to be used within the elastic range. It is considered that the required plastic deformation capacity is set to zero (plastic modulus 1.0), whereby the flange breadth-thickness ratio B/(2×t₂) makes the numerical range shown in JIS G 3192 or JP-A-2002-88974, i.e., the upper limit 10.0 of the flange breadth-thickness ratio B/(2×t₂) into a minimum value. However, in addition to this value, the flange breadth-thickness ratio B/(2×t₂) is 9.4 in a graph shown by plotting various rolled H-section steels of ASTM shown in FIG. 6, and the upper limit of the flange breadth-thickness ratio is 11.1 in a graph shown by plotting various rolled H-section steels of EN standard shown in FIG. 10. Therefore, in the present embodiment, the flange breadth-thickness ratio B/(2×t₂) is made greater than 11.1.

Similarly, the web breadth-thickness ratio (H−2×t₂)/(t₁) is a numerical range shown in JIS G 3192 or Japanese Unexamined Patent Application, First Publication No. JP-A-2002-88974. That is, the upper limit of the web breadth-thickness ratio (H−2×t₂)/(t₁) is 56.6 in a graph shown by plotting various rolled H-section steels of JIS standard shown in FIGS. 1 and 4, is 63.5 in the various rolled H-section steels of ASTM shown in FIG. 6, and is 63.3 in various rolled H-section steels of BS standard which is shown in FIG. 8. Thereby, since the upper limit 63.5 of the various rolled H-section steels of ASTM standard shown in FIG. 6 is the greatest, in the present embodiment, the upper limit of the web breadth-thickness ratio is made greater than the upper limit 63.5 of the various rolled H-section steels of ASTM standard.

As upper limits of the flange breadth-thickness ratio B/(2×t₂) and web breadth-thickness ratio (H−2×t₂)/(t₁) of the rolled H-section steel 1 in the present embodiment, the web breadth-thickness ratio (H−2×t₂)/(t₁) is set to 71.0 or less because the flange breadth-thickness ratio B/(2×t₂) becomes 15.5 or less when the tensile strength is 400 to 510 N/mm² and the design yield stress F of a steel material is 235 N/mm². Here, the above tensile strength and the design yield strength are the limiting values (similarly specified also in AU design criteria) determined in the Building Standard Law (Notification No. 596 by Ministry of Land, Infrastructure and Transport on May 18, 2007).

As upper limits of the flange breadth-thickness ratio B/(2×t₂) and web breadth-thickness ratio (H−2×t₂)/(t₁) of the rolled H-section steel 1, when the design yield stress F of a steel material is 235 N/mm², as shown in Table 1, in AISC design criteria, the upper limit is specified as 16.5, in BS design criteria, is specified as 16.2, and, in EN design criteria, is specified as 14.0, and EN design criteria in Europe are the severest design criteria. From this, 14.0 is adopted as the flange breadth-thickness ratio B/(2×t₂) of the rolled H-section steel in the present embodiment. This value is generalized as 215√{square root over ( )}(F), using the design yield stress F.

When an allowable stress is designed, the web breadth-thickness ratio (H−2×t₂)/(t₁) of the rolled H-section steel is not specified in the AISC design criteria and BS design criteria, but is specified as 124.0 in the EN design criteria. From this, in the present embodiment, 71.0 of the web breadth-thickness ratio (H−2×t₂)/(t₁) specified in AIJ design criteria is adopted. This value is generalized as 1100/√{square root over ( )}(F), using the design yield stress F.

TABLE 1 Breadth-thickness ratio in various allowable stress designs (When the design yield stress F of a steel material is 235 N/mm²) (Reference) Elastic local In the case of allowable stress design buckling AIJ AISC BS EN theoretical *1 *2 *3 *4 value Flange 15.5 16.5 16.2 14.0 18.3 breadth-thickness ratio (B/(2 × t₂)) Web 71.0 — — 124.0 56.2 breadth-thickness ratio (H-2 × t₂)/(t₁) *1: AIJ design criteria (Steel structure design criteria: Architectural Institute of Japan) *2: AISC design criteria (STEEL CONSTRUCTION MANUAL: American Institute of Steel Construction) *3: BS design criteria (BS5950: British Standard) *4: EN design criteria (EN1993-1-1: European Standard)

If flanges and a web that constitute a rolled H-section steel are considered to be a plate element and the elastic local-buckling strength σcr and specified values in respective countries are discussed, the elastic local-buckling theoretical value of a plate is obtained by the following Expression (2).

σcr=k×(π² ×E)/(12×(1−ν²))×(t/b)²  (2)

Here, k is the buckling coefficient, E is the Young's modulus, ν is the Poisson's ratio, t is the plate thickness, and b is the plate breadth.

In the rolled H-section steel, when it is made ideal that the flanges are rectangular plates with three-edges simply supported and one edge of freedom (buckling coefficient k=0.425), and a web is a rectangular plate (buckling coefficient k=4.00) with edges simply supported, in order for these elements not to cause local buckling up to yield stress, σcr=F is set, and the above Expression (2) is simplified as follows.

Since t=t₂ and b=B are established when (in the case of the flanges) the three-three edges simply supported and one edge of freedom, (B/t₂)=281/√{square root over ( )}(F) is obtained. From this, 18.3 described in the above Table 1 can be obtained as a theoretical value.

Additionally, since t=t₁ and b=H are established in the case of the edges simply supported (in the case of the web), (H/t₁)=862/√{square root over ( )}(F) is satisfied. From this, 56.2 described in the above Table 1 can be obtained as a theoretical value.

The rolled H-section steel has a cross-sectional shape in which lateral buckling and bending torsion buckling tend to occur. In particular, the flanges are the most important parts in order to secure the proof stress of a beam. From this, the flange breadth-thickness ratio is set a little more severely than the elastic local buckling. In the case of the three-edges simply supported and one edge of freedom (in the case of the flanges), the flange breadth-thickness ratio is 14.0 in an allowable stress design. Thus, the value of X is obtained such that the value of (B/t₂)=X√{square root over ( )}(F) becomes 14.0, and is generalized using (B/t₂)=215/√{square root over ( )}(F) and the design yield stress F.

Additionally, in a beam using the rolled H-section steel, it is understood that reduction in a full plastic moment caused by a shear force can be ignored unless the acting shear force exceeds the full plastic shear proof stress of the web. Therefore, the web is formed as follows so that the web breadth-thickness ratio becomes a little gentler than the elastic local buckling.

In the case of the edges simply supported (in the case of the web), the web breadth-thickness ratio is 71.0 in an allowable stress design. Thus, the value of Y is obtained such that the value of (H/t₁)=Y/√{square root over ( )}(F) becomes 71.0, and is generalized using (H/t₁)=1100/√{square root over ( )}(F) and the design yield stress F (N/mm²).

Accordingly, by specifying the relationship between the length B of the side that is the breadth of the flanges, and the flange thickness t₂ as

11.1<B/(2×t ₂)≦215/√{square root over ( )}(F)  (3),

in countries that specify the flange breadth-thickness ratio B/(2×t₂), it is possible to provide a rolled H-section steel in which dimension setting is also easy, in small-breadth and middle-breadth rolled H-section steels that have performances greater than or equal to required cross-sectional performance, while reducing the weight of steel in a rolled H-section steel with new cross-sectional shape.

Additionally, in countries that specify the web breadth-thickness ratio (H−2×t₂), as described above, the relationship between the height (H), the web thickness t₁ and the flange thickness t₂ is defined as

56.6<(H−2×t ₂)/t≦1100/√{square root over ( )}(F)  (4),

when the design yield stress F (N/mm²) is 235≦F≦275.

On the other hand, by making the flange breadth-thickness ratio B/(2×t₂) and the web breadth-thickness ratio (H−2×t₂)/(t₁) greater than before, the height H of a cross-section and the dimension B of the side in the rolled H-section steel 1 can be increased. Therefore, even when the web thickness t₁ is equal to or slightly smaller than the flange thickness t₂, the cross-sectional secondary moment (I) per unit cross-sectional area and a section modulus (Z) for resisting a bending stress can be made higher than a conventional case, to improve rigidity (especially, around a strong axis).

Hence, the web thickness and flange thickness ratio (t₁/t₂) can be made greater than a numerical range shown in JIS G 3192, i.e., the upper limit 0.75 of the web thickness to flange thickness ratio (t₁/t₂).

Accordingly, in the present embodiment, the lower limit of the web thickness to flange thickness ratio (t₁/t₂) is made greater than 0.75.

In addition, since the efficiency of the cross-sectional secondary moment I and the section modulus Z to weight degrades if the web thickness t₁ becomes greater than or equal to than the flange thickness t₂, the web thickness and flange thickness ratio (t₁/t₂) is set to less than 1.0.

Accordingly, in the rolled H-section steel 1 of the present embodiment, as upper and lower values of the web thickness and flange thickness ratio (t₁/t₂),

0.75<(t ₁ /t ₂)<1.0 is defined  (5).

In consideration of the above points, various rolled H-section steels 1 of the present embodiment set to various dimensions are shown in Table 3 as Examples A to H of the invention. A cross-sectional dimension, the side-height ratio (B/H), the flange breadth-thickness ratio B/(2×t₂), the web breadth-thickness ratio (H−2×t₂)/(t₁), the web thickness to flange thickness ratio (t₁/t₂), and the cross-sectional performance are shown in Table 3. Additionally, in Table 3, various conventional rolled H-section steels 2 in Japan corresponding to the examples A to H of the invention are shown together in Table 3 as conventional examples A to H. Additionally, a cross-sectional area ratio, a cross-sectional secondary moment ratio around a strong axis, and a section modulus ratio around a strong axis in the examples A to H of the invention and the conventional examples A to H corresponding thereto are shown in Table 3.

In addition, on the coordinate axes shown in FIG. 1 in which the flange breadth-thickness ratio has on the horizontal axis and the web breadth-thickness ratio has on the vertical axis, if the travel distance (absolute number) from the conventional example A (to H) to the example A (to H) of the invention is calculated for the respective examples, the results are as follows. In the examples A and B (travel distance>30 on the coordinate axes in the horizontal axis: flange breadth-thickness ratio and the vertical axis: web breadth-thickness ratio) of the invention, it is understood that the cross-sectional secondary moment ratios become larger as the travel distances (absolute number) of the examples A and B become larger than those of the examples C to H (travel distance<25 on the same coordinate axes), i.e., the breadth and height of a H-shaped cross-section increase.

Travel distance from conventional examples to Cross-sectional secondary Examples examples of the invention moment ratio A 33.3 1.61 B 31.8 1.39 C 23.6 1.17 D 21.3 1.23 E 18.4 1.18 F 23.1 1.21 G 22.0 1.14 H 19.7 1.14

TABLE 2-1 Web thickness Sectional dimension Flange Web to flange Nominal Web Flange Curvature Side-height breadth-thickness breadth-thickness thickness dimension Height Side thickness breadth radius ratio ratio ratio ratio Height × Side H mm B mm t₁ mm t₂ mm r mm B/H B/(2 × t₂) (H-2 × t₂)/t₁ t₁/t₂ 100 × 50  100 50 5 7 8 0.50 3.6 17.2 0.71 100 × 100 100 100 6 8 8 1.00 6.3 14.0 0.75 125 × 60  125 60 6 8 8 0.48 3.8 18.2 0.75 125 × 125 125 125 6.5 9 8 1.00 6.9 16.5 0.72 150 × 75  150 75 5 7 8 0.50 5.4 27.2 0.71 150 × 100 148 100 6 9 8 0.68 5.6 21.7 0.67 150 × 150 150 150 7 10 8 1.00 7.5 18.6 0.70 175 × 90  175 90 5 8 8 0.51 5.6 31.8 0.63 175 × 175 175 175 7.5 11 13 1.00 8.0 20.4 0.68 200 × 100 198 99 4.5 7 8 0.50 7.1 40.9 0.64 200 100 5.5 8 8 0.50 6.3 33.5 0.69 200 × 150 194 150 6 9 8 0.77 8.3 29.3 0.67 200 × 200 200 200 8 12 13 1.0 8.3 22.0 0.67 200 204 12 12 13 1.02 8.5 14.7 1.00 250 × 125 248 124 5 8 8 0.50 7.8 46.4 0.63 250 125 6 9 8 0.50 6.9 38.7 0.67 250 × 175 244 175 7 11 13 0.72 8.0 31.7 0.64 250 × 250 250 250 9 14 13 1.00 8.9 24.7 0.64 250 255 14 14 13 1.02 9.1 15.9 1.00

TABLE 2-2 Web thickness Sectional dimension Flange Web to flange Nominal Web Flange Curvature Side-height breadth-thickness breadth-thickness thickness dimension Height Side thickness breadth radius ratio ratio ratio ratio Height × Side H mm B mm t₁ mm t₂ mm r mm B/H B/(2 × t₂) (H-2 × t₂)/t₁ t₁/t₂ 300 × 150 298 149 5.5 8 13 0.50 9.3 51.3 0.69 300 150 6.5 9 13 0.50 8.3 43.4 0.72 300 × 200 294 200 8 12 13 0.68 8.3 33.8 0.67 300 × 300 294 302 12 12 13 1.03 12.6 22.5 1.00 300 300 10 15 13 1.00 10.0 27.0 0.67 300 305 15 15 13 1.02 10.2 18.0 1.00 350 × 175 346 174 6 9 13 0.50 9.7 54.7 0.67 350 175 7 11 13 0.50 8.0 46.9 0.64 350 × 250 340 250 9 14 13 0.74 8.9 34.7 0.64 350 × 350 344 348 10 16 13 1.01 10.9 31.2 0.63 350 350 12 19 13 1.00 9.2 26.0 0.63 400 × 200 396 199 7 11 13 0.50 9.0 53.4 0.64 400 200 8 13 13 0.50 7.7 46.8 0.62 400 × 300 390 300 10 16 13 0.77 9.4 35.8 0.63 400 × 400 388 402 15 15 22 1.04 13.4 23.9 1.00 394 398 11 18 22 1.01 11.1 32.5 0.61 400 400 13 21 22 1.00 9.5 27.5 0.62 400 408 21 21 22 1.02 9.7 17.0 1.00 414 405 18 28 22 0.98 7.2 19.9 0.64 428 407 20 35 22 0.95 5.8 17.9 0.57 458 417 30 50 22 0.91 4.2 11.9 0.60 498 432 45 70 22 0.87 3.1 8.0 0.64 450 × 200 446 199 8 12 13 0.45 8.3 52.8 0.67 450 200 9 14 13 0.44 7.1 46.9 0.64 450 × 300 440 300 11 18 13 0.68 8.3 36.7 0.61

TABLE 2-3 Web thickness Sectional dimension Flange Web to flange Nominal Web Flange Curvature Side-height breadth-thickness breadth-thickness thickness dimension Height Side thickness breadth radius ratio ratio ratio ratio Height × Side H mm B mm t₁ mm t₂mm r mm B/H B/(2 × t₂) (H-2 × t₂)/t₁ t₁/t₂ 500 × 200 496 199 9 14 13 0.40 7.1 52.0 0.64 500 200 10 16 13 0.40 6.3 46.8 0.63 506 201 11 19 13 0.40 5.3 42.5 0.58 500 × 300 482 300 11 15 13 0.62 10.0 41.1 0.73 488 300 11 18 13 0.61 8.3 41.1 0.61 600 × 200 596 199 10 15 13 0.33 6.6 56.6 0.67 600 200 11 17 13 0.33 5.9 51.5 0.65 606 201 12 20 13 0.33 5.0 47.2 0.60 600 × 300 582 300 12 17 13 0.52 8.8 45.7 0.71 588 300 12 20 13 0.51 7.5 45.7 0.60 594 302 14 23 13 0.51 6.6 39.1 0.61 700 × 300 692 300 13 20 18 0.43 7.5 50.2 0.65 700 300 13 24 18 0.43 6.3 50.2 0.54 800 × 300 792 300 14 22 18 0.38 6.8 53.4 0.64 800 300 14 26 18 0.38 5.8 53.4 0.54 900 × 300 890 299 15 23 18 0.34 6.5 56.3 0.65 900 300 16 28 18 0.33 5.4 52.8 0.57 912 302 18 34 18 0.33 4.4 46.9 0.53 B/H is in a range of 0.77 or less Minimum 3.6 17.2 0.53 value Maximum 10.0 56.6 0.75 value B/H is in a range exceeding 0.77 Minimum 3.1 8.0 0.57 value Maximum 13.4 32.5 1.00 value

TABLE 3 Cross-sectional perforamance of examples (F235Ns/m²) Web Cross-sectional Section Flange Web thickness secondary modulus Side- breadth- breadth- and flange Cross- moment ratio arund height thickness thickness thickness sectional around strong strong Sectional dimension ratio ratio ratio ratio area axis axis H × B × t₁ × t₂(×r) mm B/H B/(2 × t₂) (H-2 × t₂)/t₁ t₁/t₂ A cm² I cm⁴ Z cm³ Example A H-275 × 120 × 4 × 5(×8) 0.44 12.0 66.3 0.80 23.15 2901 211 of the invention Conventional H-200 × 100 × 5.5 × 8(×8) 0.50 6.3 33.5 0.69 26.67 1806 181 example A Example A — — — — — 0.87 1.61 1.17 of the invention/ Conventional example A Example B H-325 × 150 × 4.5 × 5.5(×8) 0.46 13.6 69.8 0.82 31.18 5505 339 of the invention Conventional H-250 × 125 × 6 × 9(×8) 0.50 6.9 38.7 0.67 36.97 3965 317 example B Example B — — — — — 0.84 1.39 1.07 of the invention/ Conventional example B Example C H-345 × 175 × 5 × 6.5(×13) 0.51 13.5 66.4 0.77 40.80 8428 489 of the invention Conventional H-300 × 150 × 6.5 × 9(×13) 0.50 8.3 43.4 0.72 46.78 7209 481 example C Example C — — — — — 0.87 1.17 1.02 of the invention/ Conventional example C Example D H-420 × 200 × 6 × 7.5(×13) 0.48 13.3 67.5 0.80 55.75 16663 793 of the invention Conventional H-350 × 175 × 7 × 11(×13) 0.50 8.0 46.9 0.64 62.91 13500 771 example D Example D — — — — — 0.89 1.23 1.03 of the invention/ Conventional example D Example E H-470 × 225 × 7 × 9(×13) 0.48 12.5 64.6 0.78 73.59 27629 1176 of the invention Conventional H-400 × 200 × 8 × 13(×13) 0.50 7.7 46.8 0.62 83.37 23457 1173 example E Example E — — — — — 0.88 1.18 1.00 of the invention/ Conventional example E Example F H-540 × 225 × 7.5 × 9.5(×13) 0.42 11.8 69.5 0.79 83.28 39883 1477 of the invention Conventional H-450 × 200 ×9 × 14(×13) 0.44 7.1 46.9 0.64 95.43 32887 1462 example F Example F — — — — — 0.87 1.21 1.01 of the invention/ Conventional example F Example G H-560 × 275 × 8 × 10(×13) 0.49 13.8 67.5 0.80 99.65 53131 1898 of the invention Conventional H-500 × 200 × 10 × 16 × (13) 0.40 6.3 46.8 0.63 112.25 46811 1872 example G Example G — — — — — 0.89 1.14 1.01 of the invention/ Conventional example G Example H H-680 × 275 × 9.5 × 10(×13) 0.40 13.8 69.5 0.95 119.15 86041 2531 of the invention Conventional H-600 × 200 × 11 × 17(×13) 0.33 5.9 51.5 0.65 131.71 75557 2519 example H Example H — — — — — 0.90 1.14 1.00 of the invention/ Conventional example H

As in the cross-sectional performance of the present embodiment shown in Table 3, the examples A to H of the invention are rolled H-section steels for a small beam. In all of the examples, the side-height ratio becomes 0.51 or less, the flange breadth-thickness ratio becomes 11.8 to 13.8, the web breadth-thickness ratio becomes 64.6 to 69.8, and the web thickness and flange thickness ratio becomes 0.77 to 0.95 or less.

Additionally, if the examples A to H of the invention that are rolled H-section steels of the present embodiment in Table 3 and the conventional examples A to H that are conventional rolled H-section steels corresponding thereto are compared with each other, compared to the conventional examples, in the examples A to H of the invention that are rolled H-section steels of the present embodiment in which the web thickness t₁ and flange thickness t₂ are made small, and the height H and the dimension B of the side that is the flange breadth, it is understood that the cross-sectional area A can be reduced by 10% to 16%, the cross-sectional secondary moment (I) ratio around a strong axis can exhibit a performance improvement of 14% to 61%, and the section modulus (Z) ratio around a strong axis can exhibit a performance improvement of 17%. In addition, in Tables 2-1 to 2-3, it is understood that the minimum of the side-height ratio (B/H) is 0.33.

Additionally, as can be seen from FIG. 1, on the graph of the flange breadth-thickness ratio and the web breadth-thickness ratio, it is understood that the rolled H-section steels 1 including the examples A to H of the invention that satisfy respective conditions of the above Expressions (1), (3), and (4) of the present embodiment are rolled H-section steels in a region that can be clearly distinguished from a region of conventional well-known rolled H-section steels in Japan and other countries (refer to FIGS. 1, 6, 8, and 10).

Additionally, as can be seen from FIG. 2, on the graph of the side-height ratio (B/H) and the web thickness to flange thickness ratio (t₁/t₂), it is understood that the rolled H-section steels 1 including the examples A to H of the invention that satisfy conditions of the above Expressions (1), (3), and (4) of the present embodiment are rolled H-section steels in a region that can be clearly distinguished from a region of conventional well-known rolled H-section steels in Japan and other countries (refer to FIGS. 2, 7, 9, and 11).

Additionally, as can be seen from Table 3 and FIGS. 1 and 2, the rolled H-section steel 1 whose dimensions are set as in the present embodiment exhibits a markedly excellent cross-sectional performance compared to the conventional well-known rolled H-section steel.

FIG. 1 and Table 3 show the cross-sectional performance of the examples of the present embodiment and the conventional examples when the specified design strength F of a steel material is 235 N/mm². Next, similarly to the above embodiment, the cross-sectional performance of the examples of the present embodiment in a case where the specified design strength F of the steel material (N/mm²) is 235≦F≦275 and the concrete specific specified design strength F is 275 N/mm², will be described, in comparison to the conventional examples.

As described above, if the rolled-H-section steel for a small beam is adopted, the rolled H-section steel remains in use within the elastic range. Therefore, the required plastic deformation capacity of a beam member is zero (plastic modulus 1.0), which is sufficient. Hence, the flange breadth-thickness ratio and the web breadth-thickness ratio are made greater than the numerical ranges (the upper limit of the flange breadth-thickness ratio is 11.1, and the upper limit of the web breadth-thickness ratio is 63.5) shown in JIS G 3192, JP-A-2002-88974, EN standard, or ASTM standard. The upper limits of the flange breadth-thickness ratio B/(2×t₂) and web breadth-thickness ratio (H−2×t₂)/(t₁) of the rolled H-section steel 1 in the present embodiment, may satisfy the limiting values determined in the Building Standard Law (Notification No. 596 by Ministry of Land, Infrastructure and Transport on May 18, 2007), and satisfy AISC design criteria, BS design criteria, and EN design criteria. That is, when the tensile strength is 400 to 510 N/mm² (the specified design strength F of a steel material is 235 N/mm²), the flange breadth-thickness ratio B/(2×t₂) is less than or equal to 215√{square root over ( )}(F) (i.e., less than or equal to 14.0), and the web breadth-thickness ratio (H−2×t₂)/(t₁) is less than or equal to 1100/√{square root over ( )}(F) (i.e., less than or equal to 71.0). Thus, when the tensile strength is 400 to 510 N/mm² (the specified design strength F of a steel material is 235≦F≦275 N/mm²), and the design yield stress is F, the flange breadth-thickness ratio B/(2×t₂) may be less than or equal to 215/√{square root over ( )}(F), and the web breadth-thickness ratio (H−2×t₂)/(t₁) may be less than or equal to 1100/√{square root over ( )}(F).

For example, when the design yield stress F is 275 N/mm², the flange breadth-thickness ratio B/(2×t₂) may be less than or equal to 215/√{square root over ( )}275 (i.e., less than or equal to 12.9), and the web breadth-thickness ratio (H−2×t₂)/(t₁) may less than or equal to 1100/√{square root over ( )}(275) (i.e., less than or equal to 66.0).

The rolled H-section steel and the dimensions of the parts in the present embodiment in which it is required that the design yield stress F (N/mm²) of the steel material as described above satisfies 235≦F≦275 N, are set as follows.

A rolled H-section steel may be adopted in which the relationship between the height (H) and the length (B) of the side that is the flange breadth in the rolled H-section steel is

(B/H)≦0.77  (6),

the tensile strength which is 400 to 510 N/mm², and the relationship between the length B of the side and the flange thickness t₂ is defined as

11.1<B/(2×t ₂)≦215/√{square root over ( )}(F)  (7).

Additionally, depending on the case, a rolled H-section steel may be adopted that satisfies the above conditions, and in which the relationship between the height H and the web thickness t₁, and the flange thickness t₂ is defined as

63.6<((H−2×t ₂)/t ₁)≦1100/√{square root over ( )}(F)  (8),

(where F is the specified design strength (N/mm²) of the steel material and 235≦F≦275).

Additionally, depending on the case, a rolled H-section steel may be adopted that satisfies the above conditions and in which the relationship between the web thickness t₁ and the flange thickness t₂ is

0.75<(t ₁ /t ₂)<1.0  (9).

For example, in a case where the specified design strength F of a steel material is 275 N/mm², under the conditions described above, various rolled H-section steels 1 of the present embodiment set to various dimensions are shown in Table 4 as Examples A to H of the invention. A cross-sectional dimension, the side-height ratio (B/H), the flange breadth-thickness ratio B/(2×t₂), the web breadth-thickness ratio (H−2×t₂)/(t₁), the web thickness and flange thickness ratio (t₁/t₂), and the cross-sectional performance are shown in Table 4. Additionally, in Table 4, various conventional rolled H-section steel 2 corresponding to the examples A to H of the invention are together shown as conventional examples A to H. Additionally, a cross-sectional ratio, a cross-sectional secondary moment ratio around a strong axis, and a section modulus ratio around a strong axis in the examples A to H of the invention and the conventional examples A to H corresponding thereto are shown in Table 4.

TABLE 4 Cross-sectional performance of examples (F235Ns/m²) Web Cross-sectional Section Flange Web thickness secondary modulus Side- breadth- breadth- to flange Cross- moment ratio around height thickness thickness thickness sectional around strong strong Sectional dimension ratio ratio ratio ratio area axis axis H × B × t₁ × t₂(×r) mm B/H B/(2 × t₂) (H-2 × t₂)/t₁ t₁/t₂ A cm² I cm⁴ Z cm³ Example A H-275 × 120 × 4.5 × 5(×8) 0.44 12.0 58.9 0.90 24.47 2979 217 of the invention Conventional H-200 × 100 × 5.5 × 8(×8) 0.50 6.3 33.5 0.69 26.67 1806 181 example A Example A — — — — — 0.92 1.65 1.20 of the invention/ Conventional example A Example B H-310 × 150 × 5 × 6(×8) 0.48 12.5 59.6 0.83 33.45 5381 347 of the invention Conventional H-250 × 25 × 6 × 9(×8) 0.50 6.9 38.7 0.67 36.97 3965 317 example B Example B — — — — — 0.90 1.36 1.09 of the invention/ Conventional example B Example C H-340 × 175 × 5.5 × 7 (×13) 0.51 12.5 59.3 0.79 43.88 8753 515 of the invention Conventional H-300 × 150 × 6.5 × 9(×13) 0.50 8.3 43.4 0.72 46.78 7209 481 example C Example C — — — — — 0.94 1.21 1.07 of the invention/ Conventional example C Example D H-400 × 200 × 6.5 × 8(×13) 0.50 12.5 59.1 0.81 58.41 15881 794 of the invention Conventional H-350 × 175 × 7 × 11(×13) 0.50 8.0 46.9 0.64 62.91 13500 771 example D Example D — — — — — 0.93 1.18 1.03 of the invention/ Conventional example D Example E H-470 × 225 × 7.5 × 9(×13) 0.48 12.5 60.3 0.83 75.85 28014 1192 of the invention Conventional H-400 × 200 × 8 × 13(×13) 0.50 7.7 46.8 0.62 83.37 23457 1173 example E Example E — — — — — 0.91 1.19 1.02 of the invention/ Conventional example E Example F H-520 × 225 × 8.5 × 10(×13) 0.43 11.3 58.5 0.85 88.95 39005 1500 of the invention Conventional H-450 × 200 × 9 × 14(×13) 0.44 7.1 46.9 0.64 95.43 32887 1462 example F Example F — — — — — 0.93 1.19 1.03 of the invention/ Conventional example F Example G H-570 × 250 × 9 × 10.5(×13) 0.44 11.9 61.0 0.86 103.36 54572 1915 of the invention Conventional H-500 × 200 × 10 × 16 × (13) 0.40 6.3 46.8 0.63 112.25 46811 1872 example G Example G — — — — — 0.92 1.17 1.02 of the invention/ Conventional example G Example H H-625 × 275 × 10 × 11.5(×13) 0.44 12.0 60.2 0.87 124.90 78992 2528 of the invention Conventional H-600 × 200 × 11 × 17(×13) 0.33 5.9 51.5 0.65 131.71 75557 2519 example H Example H — — — — — 0.95 1.05 1.00 of the invention/ Conventional example H

As in the cross-sectional performance of the examples of the present embodiment shown in Table 4, the examples A to H of the invention are rolled H-section steel for a small beam. In all of the examples, the side-height ratio becomes 0.51 or less, the flange breadth-thickness ratio becomes 11.3 to 12.5, the web breadth-thickness ratio becomes 58.5 to 61.0, and the web thickness and flange thickness ratio becomes 0.79 to 0.90.

Additionally, if the examples A to H of the invention that are rolled H-section steel of the present embodiment in Table 4 and the conventional examples A to H that are conventional rolled H-section steel corresponding thereto are compared with each other, compared to the conventional examples, in the examples A to H of the invention that are rolled H-section steel of the present embodiment in which the web thickness t₁ and flange thickness t₂ are made small, and the height H and the dimension B of the side that is the flange breadth, it is understood that the cross-sectional area A can be reduced by 5% to 10%, the cross-sectional secondary moment (I) ratio around a strong axis can exhibit a performance improvement of 5% to 65%, and the section modulus (Z) ratio around a strong axis can exhibit a performance improvement which at least the same as before, and the best achieves improvement of 20%.

The rolled H-section steel 1 of the present embodiment can also be applied to a small-breadth beam, a middle-breadth small beam, and a middle-breadth beam in addition to the small-breadth small beam.

INDUSTRIAL APPLICABILITY

According to the invention, compared to rolled H-section steel that is standardized in major advanced nations including the U.S., Britain, Europe, and Japan, it is possible to provide a rolled H-section steel that is made to be lightweight for a small beam and does not degrade the cross-sectional performance.

REFERENCE SIGNS LIST

-   -   1: Rolled H-section steel of Present Embodiment     -   2: Conventional rolled H-section steel     -   3: Web     -   4: Flange 

1. A rolled H-section steel having a web and flanges, wherein: the rolled H-section steel satisfies a following Expression (1) when H is a height of the rolled H-section steel, and B is a breadth of the flanges; a tensile strength thereof is 400 to 510 N/mm²; and the rolled H-section steel satisfies following Expressions (2) and (3), when a plate thickness of the flanges is t₂ and a design yield stress of a steel material of the rolled H-section steel is F (N/mm²). (B/H)≦0.77  (1) 11.1<B/(2×t ₂)≦215/√{square root over ( )}(F)  (2) 235≦F≦275  (3)
 2. The rolled H-section steel according to claim 1, wherein the rolled H-section steel satisfies a following Expression (4) when a plate thickness of the web is t₁. 63.5<((H−2×t ₂)/t ₁)≦1100/√{square root over ( )}(F)  (4)
 3. The rolled H-section steel according to claim 1, wherein a plate thickness t₁ of the web and the plate thickness t₂ of the flanges satisfy a following Expression (5). 0.75<(t ₁ /t ₂)<1.0  (5) 